Over the past 6 to 8 weeks I've had various renewal offers shown in MVM. The latest is a 'final offer' and it's £15 a month more than the last offer shown in MVM. My current discounted pricing isn't due to end until November so no doubt I will receive more offers.
VM's actual prices can vary on a day to day basis, and agent to agent basis. I know it sounds odd, but agents are given a set amount of allowances to offer at varying price points, and also dependant upon department. Offers made via MVM aren't available to the webteam, retentions or normal telephone agents.
If agents have used up their quota of lowest prices for the day or week, then they wouldn't be able to offer say the Mega Volt bundle for £100, but if the next agent hadn't reached their quota then they would be able to offer that price point, or possibly even lower. It's also possible that one of the retention teams may be "trialling" a price point not available to other teams.
To be honest if you are fairly happy with a quoted price whilst on the phone with the agent (or need to confirm it first with say your partner) then accept it as it probably won't be available again. You can then take advantage of the 14 day distance selling window should you change your mind and wish to reject that offer. You would then go back to your original pricing, even if it was the out of contract price, and package (or nearest equivalent) and then have the option of either cancelling or renegotiating.
You might receive contact from the 'winback team' (outbound retentions) with a better offer now that you've placed your cancellation request, however that's not guaranteed, and won't happen if you've opted out of marketing. To check this I suggest signing into MVM and checking under Account Settings > Marketing & Contact Preferences.
Under the Marketing Consent sub heading is a box that reads, 'Sounds good! Keep me up to date' Make sure that the box next to it has a tick in it, otherwise you definitely won't receive a callback. If you do need to update those preferences be sure to click on Save Changes.